The Minnesota Vikings' rookie quarterback threw two interceptions in a seven-on-seven passing drill, completed only one pass in a pair of move-the-ball drives and generally seemed a little off the mark in his second fully-padded NFL practice.

"It's called being a rookie in the National Football League," coach Leslie Frazier said. "There's going to be some other days like that. That's part of it. You guys have been around long enough. You know. He's going to have a lot of good days, too."

Ponder, who called his performance "a step back," once again took the second-team reps ahead of Joe Webb in part because coaches want their top draft pick working with a better offensive line.

He completed 4 of 8 passes in team (11-on-11) drills and had a surprising amount of trouble in 7-on-7, going 5-for-10 with two interceptions in a drill that favors the offense.

"It was our first kind of day of situational stuff, working on some third-down stuff and first day that we went full go on some things," Ponder said. "I think it was definitely good to get that out of the way and learn from it. We obviously have got a lot of film to watch and those days are where you progress the most from."

Both interceptions were intended for fellow rookie Stephen Burton, who took his routes up the field as Ponder tried to throw underneath coverage. But Ponder took full responsibility, while also acknowledging his grasp of Musgrave's offense remains a work in progress.

"I threw two bad balls," Ponder said. "I could have thrown some better balls and it wouldn't have happened."

The other quarterbacks weren't much better. Starter Donovan McNabb's two move-the-ball drives generated only one first down, and Joe Webb threw incomplete on all three of his passes in 11-on-11.

Peterson gets physical

Friday's afternoon practice was the first to feature live tackling, and Adrian Peterson was right in the middle of it.

Safety Tyrell Johnson sliced through the line on the first play of a short-yardage drill and cut down Peterson behind the line -- something the All-Pro halfback hasn't experienced much in training camp during his career.

Frazier said running backs coach James Saxon asked permission before putting Peterson into the drill, and Frazier gave him a thumbs-up.

"Hopefully, it'll pay off for us," Frazier said. "We'll have to watch some things during the preseason. It won't happen that often, but it's part of what we do for a living. It's tackling. It's hitting. It's running. It's football."

Health watch

Cornerback Cedric Griffin could be available as soon as the Vikings' second preseason game on Aug. 20 at Seattle, Frazier said, while right guard Anthony Herrera is at least an additional week or two away.

Both players are recovering from knee reconstruction, and the goal is to have them ready for the regular-season opener on Sept. 11 at San Diego. Griffin's injury occurred more than a month earlier than Herrera's last fall, though, and he's been practicing with the first-team defense while Herrera rehabs on the camp/physically unable to perform list.

If Herrera can't play in a preseason game, Frazier indicated there's no way he'd be cleared for the opener -- opening an opportunity for Chris DeGeare or perhaps Ryan Cook to win the starting job out of camp.

"We don't know what's going to happen with Anthony," Frazier said. "One of the reasons we signed Ryan was not just to be a backup guy because he can swing, but to give us some competition at the right guard position. He did some things down the stretch (last season) to make me think that he can compete for that job. Chris will have to step it up and compete."

Frazier said he doesn't think the triceps on which Herrera also had surgery is an issue.

Peterson took responsibility for his well-publicized remark about the NFL being "modern-day slavery," saying the remark was taken "out of context, and it was on me for putting it out there to make it available to be taken out of context."

He made the remark to a Yahoo! Sports reporter in March and hadn't addressed it since. Frazier didn't say much about it, Peterson said, adding he believes it's a dead issue.

"I regret using those words, because obviously, there's nothing -- absolutely nothing -- that you can compare to slavery," Peterson said. "It stands alone. It's something that I should have used better wording to put that out there. But it's spoiled milk, it's old and it's over with."

Quick hits

• With three veteran receivers finally eligible to practice, the Vikings released undrafted rookie Ryan Lincoln and signed Colby Whitlock, a 6-foot-3, 294-pound rookie defensive tackle from Texas Tech.

• Referee Jeff Triplette and other NFL officials gave their annual presentation to Vikings players on rules changes and emphases, which for the second straight included extensive time on player safety.

• Rookie CB Marcell Gipson left the team to attend to a family emergency, Frazier said. It was unclear when he would return.